C150 : short stall warning in climb out

[alexka]

Hi All,

It was a flight with C150. Takeoff was from 645 m long paved runway. Wind at airfield was 4 KT. The airfield itself however is located on a hill and orographic winds are quite usual there, gusting sometimes. This time, the air around airfield was quite smooth, with no noticeable gusts. Aircraft was loaded, but in limits.

Takeoff was with flaps up, rotated and lifted off as usual (55 and 60 kt respectively). After several seconds in established climbout, at airspeed of 65 knots, stall warning was sounding for a very short fraction of second. There was no bank. I also didn't feel any noticeable change in how controls felt : they were effective as usual. Though the warning was there for a very short time, I pushed the column slightly gaining another 5 knots, and continued climb out at 70 kt.

My question is what could be a source of stall warning in such situation? I have a feeling it has something to do with very short local windshear which caused wing to stall for a moment, but would be interesting to know if someone else experienced similar thing.

[sternone]

I had the same situation last week during takoff in a C152, my instructor pushed the yoke directly forward, it was my fault, i was pitching up to much

[Will Hung]

Gusts of wind can activate the stall warner, as can a greaser of a landing !

[Wessex Boy]

A gust of wind/windshear can affect the angle of attack of the wing through the airflow momentarily, if the stall warner chirrups, it is best to push the stick forward and take a shallower/faster climb to reduce the effect of the windshear.

[J.A.F.O.]

as can a greaser of a landing !

That'll be why I don't hear it too often, then.

My guess would be a gust, the wing doesn't actually need to stall for the warner to sound, it normally is set to sound a little before the stall to give you time to take the correct action - as you did.

My own opinion is that it's better to be safe than sorry in this life than to be able to offer an interesting explanation in the next.

[jamestkirk]

Stall warner (JAA regs) should be regulated to go off at 5kts or 5% above the stall, whichever is the greater. I think this is a minimum requirement, but it's been a while since I sat my ATPL air law.

As the previuos posts have correctly stated. If I could remember which book it is clearly written in, I would tell you. But it's to do with vectors of wind direction and speed. If you go forward at 60kts and get up updraft of 30kts you get a resultant of x kts.

We had a similar situation here on the south coast. The r/w was changed to 20 due to a sea breeze. Although, the sea breeze was only 30-50' thick.

So every had a stonking tailwind down final until that height, then go a nice piece of windshear just before touch down, with an extra pinch of speed . People going around for about half an hour until ATC realised.

Oh how i laughed!! I wanted to send a bunch of students on a first solo. That would put hairs on their chest. :} Cruel to be kind and all that.

[FlyingForFun]

What speed does your stall warner go off at? And what IAS does your aircraft stall at, clean with the power off (I mean actually stall, not what it says in the POH)?

You should be able to find both of these numers with a short test-flight. This test-flight should be able to eliminate a couple of possiblities: the first is that your stall-warner is set to go off at too low an angle of attack (in which case you will notice, during your test flight, that the stall warner goes off quite some time before the stall occurs). The second is that your airspeed indicator is over-reading, and you were actually flying slower than you thought you were when this occured.

I suspect, though, that neither of these is the case, or you'd have noticed it before, and the most likely cause is a gust of wind, as others have said.

FFF
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[BackPacker]

There are more aircraft who give an occasional chirp from the stall warner when climbing out. It takes only a very small gust of wind when you're climbing 10-15 knots above stall speed to trigger a sensitive stall warner.

Yes, you heed the warning, so check your airspeed, give the aircraft an extra five knots, but don't panic over it.

If you fly the aircraft to the POH values for Vr, Vx, Vref and touchdown speed for short-field take-off and landing, you'll find that it's virtually impossible to do this without the occasional trigger of the stall warning.

[adverse-bump]

remember it is a stall WARNER, not a stall INDICATOR! iv heard them going off at 90kts in a PA38!

[Pilot DAR]

All good advice here, care, but don't worry about this one. Do bear in mind that in addition to the good advice here, when flying aircraft larger than the great 150, if you are climbing for prolonged periods at an airspeed low enough to chirp the stall warning, you may not be allowing the engine cooling which would be optimum. Lower the nose a little when the obsticles are cleared.

Go up high with an insructor and practice slow flight in the 150, it is amazing. With full flaps you can fly power on with the stall horn screaming and still be very safe - key words: High & Instructor.

The stall warning horn on the 150 acts as air is sucked out through it. Other aircraft types have a vane, which is actually a switch. The switch type is either on or off, or chirping in between. The 150 type is more akin to a musical instrument, and it's intensity will increase as the situation worsens. Tune your ear and go try it - high & instructor. You will learn that the first low tone is just the beginning of the fun.

Pilot DAR